Nowadays, candidates applying to tech companies such as Google or consulting firms such as McKinsey often go through a series of job interviews. These interviews are designed to assess whether a candidate is a good fit for the company and often include challenging logic brain teasers. In this article, we reveal 15 of them!
1. Estimation Brain Teaser
How many tennis balls can fit in a Formula 1 cockpit?
What it tests: estimation, assumptions, structured reasoning.
Click here to see the answer!
A standard tennis ball is about 0.07 meters, so it takes about 0.000157 m^3.
Let’s assume that a tight F1 cockpit has 0.25 m^3 of space with a packing efficiency of 50%.
Volume x Packing efficiency / Tennis ball volume = About 800 tennis balls.Note: The most important is the reasoning, not the answer accuracy.
2. Design Thinking Interview Question
Why are airplane windows rounded rather than square?
What it tests: Practical reasoning and design thinking.
Click here to see the answer!
Sharp edges of square windows create natural weak spots on the metal, which is worse with air pressure.
3. Creative Problem-Solving Brain Teaser
You are shrunk to the size of a coin, and you’re stuck in a pan with high edges. In 60 seconds, it will be set as the highest temperature. How do you survive?
What it tests: creativity, physics intuition, calm reasoning.
Click here to see the answer!
If you’re smaller, then you’ll jump at a much higher relative height. You should be able to jump higher than the pan’s walls.
4. Fermi Estimation Interview Question
How much does a taxi driver earn in a year in Amsterdam?
What it tests: Fermi estimation.
Click here to see the answer!
Let’s assume that a taxi driver does 20 ride per day in average, with an everage fare of 20 €. Taking into account their vacation, they work 5 days a week. Yearly revenue = 20 x 20 x 5 x 52 = 104 000 €Note: The most important is the reasoning, not the answer accuracy.
5. Clock Hands Logic Puzzle
How many times a week does a clock’s hand overlap?
What it tests: Calculation in an unconventional situation
Click here to see the answer!
A clock hands overlaps 11 times every 12 hours. So in one week:11 x 2 x 7 = 154 times
6. Consulting Case Interview Brain Teaser
You’re a theatre owner in the middle of NYC. You increased your marketing spending by 30%, but ticket sales stayed flat. How would you investigate?
What it tests: Lay out a plan to solve a marketing issue.
Click here to see the answer!
Investigate it as a funnel problem:1. Check the baseline and timing. Ticket sales, Seasonality, Competing events?2. Check the marketing: Clicks, website visit, completed purchases.3. Channel effectiveness: Which campaign received extra budget and which one work?4. Make hypothesis, then check with A/B testing, customer surveys, cohort analysis.Bonus answer: You can assume that the marketing increase doesn’t work because theater rooms are already full!
7. Creative Thinking Interview Riddle
One morning, you wake up to the sound of your doorbell ringing. When you open the door, you find three boxes on your doorstep, but no one is there. One box contains a penguin, one contains a frog, and one contains a fox. What do you do?
What it tests: Imagination, ability to answer quickly in a stress situation
Click here to see the answer!
You call the local zoo or wild animal shelter to figure out what to do with these animals.Or adopt all these animals and transform your rooms into terrarium.Invent any story, you just need to be confident about what you tell.
8. Business Judgment Interview Question
You own a Ferrari garage, and a customer with a Mercedes wants you to fix it, no matter the cost. Should you accept it?
What it tests: Market segment awareness
Click here to see the answer!
You don’t accept this customer, even though they are ready to pay an overcharge.Recommend them a proper garage with a towing company. That would be cheaper, and you’d keep your prestige.The bottom line is that a high standing company should always qualify their customer.
9. Market Sizing Brain Teaser
Estimate how many matcha latte cups are sold in Paris each day.
What it tests: Fermi estimation and segmentation.
Click here to see the answer!
Paris has 2 million residents, plus many commuters and tourists. Let’s assume that 300 000 people buy a café drink each day. If 3% choose a matcha latter, that’ gives around300 000 x 3% = 9000 daily matcha latte consumers in ParisNote: It tests your ability to build an estimation based on assumption. It’s ok if the result isn’t too accurate.
10. Classic Logic Puzzle: The 100 Doors
You have 100 doors in a row. You toggle every door, then every second door, then every third door, and so on. Which doors remain open?
What it tests:
Click here to see the answer!
Doors 1, 4, 9, 16, 25, 36, 49, 64, 81, and 100 remain open.A door ends up open only if it is toggled an odd number of times.Most numbers have divisors in pairs, but perfect squares have one unpaired divisor: their square root.
11. Balance Scale Logic Riddle
You have 12 balls. One is either heavier or lighter. Using a balance scale three times, find the odd ball and whether it is heavier or lighter.
What it tests: Logic
Click here to see the answer!
Label the balls 1 to 12.First weigh 1,2,3,4 against 5,6,7,8.If they balance, the odd ball is among 9,10,11,12. Weigh 9,10,11 against 1,2,3. If they balance, ball 12 is odd; weigh it against ball 1 to know if it is heavier or lighter. If 9,10,11 are heavier or lighter, weigh 9 against 10: if one side tips, that ball is the odd one with the same heavier or lighter result; if they balance, ball 11 is the odd one.If the first weighing does not balance, suppose 1,2,3,4 are heavier than 5,6,7,8. Weigh 1,2,5 against 3,6,9. If it balances, the odd ball is 4 heavy, 7 light, or 8 light; weigh 7 against 8 to decide. If the left side is heavier, the odd ball is 1 heavy, 2 heavy, or 6 light; weigh 1 against 2 to decide. If the right side is heavier, the odd ball is 3 heavy or 5 light; weigh 3 against 9 to decide.If in the first weighing 1,2,3,4 are lighter than 5,6,7,8, use the same logic with “heavy” and “light” reversed.
12. Two Doors and Two Guards Logic Riddle
You are standing in front of two doors. One door leads to the job offer, and the other leads to rejection.
There are two guards:
One guard always tells the truth.
One guard always lies.
You do not know which guard is which, and you may ask only one question to one guard.
What question should you ask to find the door that leads to the job offer?
What it tests: Logic, outside-the-box thinking, handling incomplete information
Click here to see the answer!
Ask either guard: “If I asked the other guard which door leads to freedom, what would they say?”
Whichever door they indicate will always be the wrong one.
The truthful guard reports the liar’s wrong answer, and the liar lies about the truthful guard’s right answer.
So in both cases, you should choose the opposite door.
13. Burning Ropes Logic Puzzle
You have two old ropes and a lighter.
Each rope takes exactly 1 hour to burn completely, but these old ropes do not burn at a uniform rate. For example, one half of a rope might burn in 5 minutes and the other half in 55 minutes.
Using only the two ropes and the lighter, how can you measure exactly 45 minutes?
What it tests: logic, reasoning
Click here to see the answer!
Light rope 1 at both ends and rope 2 at one end.When rope 1 burns out, 30 minutes have passed.Then light the other end of rope 2.When rope 2 burns out, 15 more minutes have passed, so the total is exactly 45 minutes.
14. Three Light Switches and Three Bulbs Logic Riddle
You are standing in a room with three light switches. In another room, there are three light bulbs.
Each switch controls exactly one light bulb, but you do not know which switch controls which bulb.
You may turn the switches on and off as much as you like, but you are allowed to enter the room with the light bulbs only once.
How can you determine which switch controls each light bulb?
What it tests: Outside-the-box thinking
Click here to see the answer!
Turn switch 1 on for a few minutes, then turn it off.Turn switch 2 on and leave switch 3 off.Enter the bulb room once.The lit bulb belongs to switch 2, the warm unlit bulb to switch 1, and the cold unlit bulb to switch 3.
15 Monty Hall Probability Brain Teaser: Should You Switch Doors?
Behind one door, there’s a car. Behind the two, there are goats. You have to choose one door. The host, who knows what is behind each door, decides to open one door to show a goat. Should you stick with your door or switch?
What it tests: Probability reasoning
Click here to see the answer!
You should switch doors.At first, your chosen door has a 1/3 chance of hiding the car, while the other two doors together have a 2/3 chance.When the host opens a goat door, that 2/3 chance transfers to the remaining unopened door.So switching gives you a 2/3 chance of winning, while staying gives only 1/3.
How to answer these questions during a job interview?
Last but not least, let’s see how you should approach them when your interviewer is challenging you with such a brain teaser.
- Clarify the question
- State assumptions explicitly
- Break the problem into parts
- Think aloud in a structured way
- Use a whiteboard or paper and a pen if available
- Check whether the answer makes sense. Feel free to correct
- Avoid rushing to the obvious answer if it seems like a trick.
The interviewer is often evaluating your reasoning process more than the final answer. It’s okay to lack accuracy; you can always improve your reasoning once you have better inputs. But the reasoning ability is what interests them.
If your job interview is tomorrow, then good luck!
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